There is known a fuel pump that sequentially draws fuel into pump chambers and thereafter sequentially discharges the fuel from the pump chambers. A fuel pump disclosed in the patent literature 1 includes: an outer gear that includes a plurality of internal teeth; an inner gear that includes a plurality of external teeth and is meshed with the outer gear while the inner gear is eccentric to the outer gear in an eccentric direction, wherein the inner gear includes a receiving hole that extends in an axial direction; a rotatable shaft that is rotationally driven; a contact portion that is formed to be contactable with the receiving hole, wherein the contact portion transmits a drive force from the rotatable shaft to the receiving hole to rotate the inner gear; and a pump housing that rotatably receives the outer gear and the inner gear. The pump housing includes a first housing component and a second housing component, between which the inner gear is held in the axial direction. When the outer gear and the inner gear are rotated to increase and decrease volumes of a plurality of pump chambers, which are formed between the outer gear and the inner gear, fuel is sequentially drawn into and is sequentially discharged from the pump chambers.
In the patent literature 1, it is assumed that the receiving hole of the inner gear and the contact portion of the coupling extend in the axial direction, and the receiving hole is urged toward a drive rotation side in a circumferential direction upon contacting of the receiving hole with the contact portion, so that the inner gear is rotated.
However, in this structure, when the inner gear is rotated, the first housing component and the second housing component, between which the inner gear is held, may be slid when the first housing component and the second housing component receive a frictional force that is equal to or larger than a certain level. Therefore, the first housing component and the second housing component need to have a predetermined degree of abrasion resistance. Thus, there is very little room for material choice of the pump housing.